The regulation of cyclic nucleotide formation and action in lung and some of its cell types including tracheal smooth muscle will be examined. The accumulation of cyclic GMP and cyclic AMP in tracheal smooth muscle induced with various hormones, neurohormones, nitroso compounds and other materials will be correlated with muscle motility and endogenous protein phosphorylation. Exogenous and endogenous protein substrates for cyclic nucleotide dependent protein kinases in lung and tracheal smooth muscle will be examined. Guanylate cyclase in lung will be characterized, purified and used to obtain antibodies that will be used to develop a radioimmunoassay for the enzyme and immunohistochemical localization of the enzyme in lung. Thus, experiments will be performed with lung and some of its cell types to determine which agents regulate the accumulation and action of cyclic nucleotides in an attempt to ascribe some functions to cyclic AMP and cyclic GMP in lung.